The present invention relates to a method for making decorative components and, more particularly, to a method for making molded decorative components having an outer elastomeric layer that is integral with an inner foam layer.
A recent trend in the automobile industry has been the development of various non-fabric automotive trim components having an elastomeric outer skin a flexible foam layer and a substrate. Among the known systems for producing decorative components are polyvinyl chloride (PVC) vacuum and rotocast systems, thermoplastic polyolefin (TPO) vacuum formed systems, thermoplastic polyurethane (TPU) rotocast systems, slush molding systems, and sprayed aliphatic urethane systems generally. However, each of the foregoing systems present certain perceived drawbacks. One drawback with all of the systems is that generally the elastomeric skin layer needs to be formed in one mold and then it has to be demolded and put into another mold for the foaming step and attachment of the substrate.
The known PVC vacuum form and rotocast systems are also undesirable because PVC is difficult to recycle and environmentally unfriendly, i.e., subject to releasing dioxins and other chlorinated by-products upon decomposition. Further, an unnecessarily thick skin is required to minimize the effects of plasticizer loss over time. PVC skins, particularly those which are vacuum formed, are often stiff and have a poor feel. Also PVC skins are prone to leaching of components into the foam backing layer.
TPO vacuum formed systems are also often stiff and have a poor feel. Further, the grain definition of the resultant components are considered to be poor in quality. Additionally, TPO skins must often be coated to improve their resistance to scratch and mar resulting in increased costs and labor.
Accordingly, U.S. Pat. No. 5,116,577 to Dabaes et al. attempted to address some of the aforementioned drawbacks seen in PVC and TPO systems, as well as certain integral skin applications by developing a method for manufacturing mold components having a relatively low density, i.e., less than 700 g/dm3. The method is said to involve applying a layer of light stable polyurethane elastomer having a predetermined color onto a mold surface by spraying and allowing it to partially cure. Thereafter, while the elastomer is still tacky, a synthetic foam composition is injected into the space of the mold cavity. Upon curing of both the elastomer layer and the synthetic foam layer, the resultant object is removed from the mold. The method of Dabaes still includes several drawbacks. For example, the disclosed use of a light stable aliphatic polyurethane elastomer for the external layer of the object is believed to greatly increase the cost of the resulting component. Additionally, the use of different chemicals for the external and foam layers necessitates the use of separate polyurethane metering machines and chemical tanks resulting in significant expense. Further, the resulting disclosed elastomer often requires additional treatment to achieve adhesion to a urethane foam. Other perceived drawbacks include poor color matching with other components, poor fogging resistance, and poor feel due to the relatively thick skins that are typically achieved in practice of the method.
It is desirable to address the leaching of materials between the layers and reduce the cost of the process by providing a method for forming a decorative component having an outer elastomeric layer that is integral with an inner foam layer wherein the elastomeric layer and the foam layer are chemically identical except for the inclusion of a blowing agent in the foam layer. It is also desirable to reduce the cost by eliminating the need to demold the elastomeric layer prior to foaming another layer behind it.
The present invention provides a method for making decorative components and, more particularly, provides a method for making molded decorative components having an outer elastomeric layer that is integral with an inner foam layer.
In one embodiment the method for forming a decorative component having an outer elastomeric layer that is integral with an inner foam layer, comprises the following steps. Forming a polyurethane mixture free of any blowing agents by combining a flow of a polyisocyanate component with a flow of a polyol component, the polyurethane mixture having a first amount of the polyisocyanate component and a first amount of the polyol component. Applying a layer of the polyurethane mixture onto a surface of a mold by flowing the polyurethane mixture through a spray nozzle directed toward the mold surface and forming an outer elastomeric layer on the mold surface. Forming a polyurethane mixture containing blowing agent by introducing a flow of water into the flow of the polyurethane mixture and changing the first amount of the polyisocyanate component to a second amount, wherein the second amount of the polyisocyanate component is greater than the first amount of the polyisocyanate component, while continuing to spray the polyurethane mixture. Directing the polyurethane mixture containing blowing agent toward the outer elastomeric layer, thereby foaming the polyurethane mixture containing blowing agent and forming an inner foam layer that is integral with the outer elastomeric layer. The decorative component is then demolded. The present invention results in a significant cost savings by eliminating the need to transfer the outer elastomeric layer to a second mold prior to introduction of the foam layer.
In a preferred embodiment the water is introduced at a flow rate that establishes a water level of between 0.3 to 3.0 percent by weight based on the total weight in the polyurethane mixture containing blowing agent.
Additional benefits and advantages of the present invention will become apparent from a reading of the description of the preferred embodiments taken in conjunction with the specific examples provided.